Recently, X-ray detectors have been widely used in medical imaging industry and been considered as the doctor's eyes. X-ray detectors can be divided into direct type X-ray detectors and indirect type X-ray detectors. Direct type X-ray detectors use a high dose of X-rays to image, which may bring the human body an additional damage. Compared with the direct type X-ray detectors, indirect type X-ray detectors use a relatively low dose of X-rays by using the PIN photodiode. Thus, indirect X-ray detectors have gradually become the mainstream of the market.
However, a surface of the PIN photodiode is defective due to the periodic damage of the N+doped layer in the PIN photodiode, resulting in a presence of a defective dark current. The defective dark current can induce a noise, which will affect the image quality. In addition, the X-ray detector may include two switching transistors (a resetting switching transistor and a row-selected switching transistor). In a resetting phase, the voltage of the N+doped layer in the PIN photodiode is reset to a power supply voltage Vdd by the resetting switching transistor. In a reading phase, a row-selected signal has a high level of Vdd, and the row-selected switching transistor may have a loss of Vth during the reading. In other words, when being irradiated by the X-rays, the PIN photodiode will generate photon electron-hole pairs. Thus, the N+doped layer in the PIN photodiode may have a voltage drop. The voltage can be completely read out by the row-selected switching transistor when the voltage drop is greater than Vth. Therefore, an additional X-ray dose is required to compensate such a Vth loss, which results in wasting the dose of X-rays.
Therefore, those skilled in the art is aimed at solving the problem of the presence of defective dark current on the surface of the PIN photodiode, thereby improving the image quality of the X-ray detector and reducing the dose of the used X-rays.